Ceramic niobate dielectric materials

ABSTRACT

A CERAMIC MATERIAL IN A PEROVSKITE STRUCTURE HAVING A HIGH DIELECTRIC PERMITTIVITY, A LOW POWER FACTOR AND A LOW TEMPERATURE COEFFICIENT OF PERMITTIVITY, THE COMPOSITION OF WHICH IS IN A CHEMICAL FORMULA OF   (BAXNA1-X) (NA0.25XNB1-0.25X)O3   WHEREIN X RANGES FROM 0.20 TO 0.95 IN ACCORDANCE WITH THE INVENTIONS. THE CERAMIC DIELECTRIC COMPOSITION OF   (BAXNA1-X) (NA0.25XNB1-0.25X)O3   CAN BE MODIFIED BY SUBSTITUTION OF SR FOR BA OR LI FOR NA IN ACCORDANCE WITH THE INVENTIONS.

Jan; 2, 1973 YOSHIHIRO MATSUO ETA 3,703,315

CERAMIC NIOBATE DIELECTRIC MATERIALS Filed June 12, 1970 YOSHIHIRO MATSUO, HIROMU SASAKI and SHIGERU HAYAKAWA, Inventars YJJJQMA Ld M Attornoys United States Patent 3,708,315 CERAMIC NIOBATE DIELECTRIC MATERIALS Yoshihiro Matsuo, Hiromu Sasaki, and Shigeru Hayakawa, Osaka, Japan, assignors to Matsushita Electric Industrial Co., Ltd., Osaka, Japan Filed June 12, 1970, Ser. No. 45,871 Claims priority, application Japan, Oct. 13, 1969, 44/81,982, 44/81,985 Int. Cl. C04b 33/00 US. Cl. 106-39 R 3 Claims ABSTRACT OF THE DISCLOSURE A ceramic material in a perovskite structure having a high dielectric permittivity, a low power factor and a low temperature coefiicient of permittivity, the composition of which is in a chemical formula of x 1 x) 0.25x 1-0.25x) 3 wherein x ranges from 0.20 to 0.95 in accordance with the inventions. The ceramic dielectric composition of can be modified by substitution of Sr for Ba or Li for Na in accordance with the inventions.

This invention relates to ceramic dielectric materials and more specially to ceramic dielectric materials in a perovskite structure, which have a high dielectric permittivity, a low power factor and a low temperature coefficient of permittivity.

Since the recent electronic industry has required miniaturization and refinement of electrical equipment, there is an increasing need for a dielectric material of a high permittivity, a low power factor and a low temperature coeflicient of permittivity. High permittivity facilitates producing a capacitor in a small physical size for a given capacitance and low power factor prevents a capacitor from being heated. Heat generation is a serious problem in miniaturized electrical equipment. Low temperature COEifiClGDt of permittivity of a capacitor enables electrical equipment or device to work in a high accuracy. It is also desired that the tempreature coefficient of permittivity can be chosen at a specific value.

Therefore, it is an object of the present invention to provide ceramic dielectric materials characterized by high permittivity and low power factor.

Another object of the present invention is to provide ceramic dielectric materials characterized by high permittivity, low power factor and a linear temperature coefiicient of permittivity.

These and other objects will be apparent upon consideration of following detailed description taken together with accompanying drawing wherein:

The figure illustrates a cross sectional view of capacitor contemplated by the present invention.

Before proceeding with a detailed description of the nature of a capacitor embodying the invention, the consrruction of such a capacitor will be described with reference to the drawing. In this drawing, character indicates generally a capacitor comprising a sintered disc 11 of dielectric material according to the invention. The sintered disc 11 is provided on two opposite surfaces with electrodes 12 and 13. The electrodes 12 and 13 may be applied to the surfaces by any suitable and available method, for example, by firing-on silver electrode paint commercially available. The disc 11 is a plate which may have any of suitable shapes, for example, circular, square or rectangular. Wire leads 15 and 16 are attached conductively to the electrodes 12 and 13, respectively by a connection means 14 such as solder or the like.

The sintered disc comprise a perovskite-type compound represented by chemical Formula 1;

x l-x) o.as i-o.zsx) s wherein x ranges from 0.2 to 0.95 in accordance with the inventions.

A sintered disc having a composition of chemical Formula 1 is in a perovskite structure and has a permittivity of to 400, a power factor lower than 10x10 and a temperature coefficient of permittivity of 50 to +800 p.p.m./ C. If the x in chemical Formula 1 is out of the range of 0.2 to 0.95, the resultant disc does not show a power factor less than l0 10- as shown in Table l.

The ceramic dielectric composition of chemical Formula 1 can be modified by substitution of Sr for Ba in accordance with the invention: The Sr-modified composition is represented by chemical Formula 2;

x 1- x) o.25 1-o.25x) 3 wherein x ranges from 0.2 to 0.95 in accordance with the invention. A sintered disc having a composition of chemical Formula 2 is in a pervoskite structure and has a permittivity of 80 to 320, a power factor lower than l0 l0- and a temperature coefiicient of permittivity of 60 to +1000 p.p.m./ C. If the x in the chemical Formula 2 is outside of the range of 0.2 to 0.95, the resultant disc does not show a power factor less than 10 10- as shown in Table 2.

The ceramic dielectric composition of chemical Formula 2 can be modified by substitution of Li for Na in accordance with the invention: The Li-modified composition is represented by chemical Formula 3;

x 1x) U.25x 1-0.25x) s wherein x ranges from 0.2 to 0.95 in accordance with the invention. A sintered disc having the composition of chemical Formula 3 is in a perovskite structure and has a permittivity of 60 to 300, a power factor lower than 10x10" and a temperature coefiicient of permittivity of 50 to +300 p.p.m./ C. If the x in chemical Formula 3 is outside of the range of 0.2 to 0.95, the resultant disc does not show a power factor less than 10 10- as shown in Table 3.

The composition in chemical Formula 1 to 3 can be prepared by mixtures of ingredient oxides in mole ratio dependent upon the chemical formulae. For example, the composition in chemical Formula 1 can be prepared by the following mixture listed in Table 4, wherein x ranges from 0.20 to 0.95. It is possible to employ, as the starting material, any compound which is converted into an oxide during firing process. Operable starting materials which may be employed in place of an oxide are, for example, carbonates, hydro-oxides, and oxalates. A given mixture is well mixed in a wet ball mill, dried, calcined, pulverized, and pressed into discs. The pressed discs are fired at a given temperature dependent upon compositions of mixtures. The Ag-electrode is attached to the both surfaces of the fired disc. Permittivity and power factor of the discs are measured at a constant applied field of I mHz as a function of temperature from to 300 C. The temperat-ure coefiicient of permittivity (u) is usually defined by the following equation:

oc=e(80 C.)e(20 C.)/e(20 C.) X (80 C.2 0 C.)

wherein e(80 C.) is a permittivity of 80 C. e(20 C.) is a permittivity of 20 C.

EXAMPLE Compositions corresponding to the chemical formulae listed in column 1 of Table 5 are prepared by using starting materials of barium carbonate, strontium carbonate, sodium carbonate, lithium carbonate, and niobium oxide.

3 The mixtures of starting materials in given compositions are intimately mixed in a wet ball mill, dried, calcined for two hours at a temperature as shown at the column 2 of the tables (first firing temperature), pulverized, and pressed at a pressure of 700 kg. per cm. into discs. The pressed discs are fired for two hours at a temperature as shown at the column 3 of the tables (final firing temperature). The permittivity and power factor at 20 C. and 1 mHz. set forth in column 4 and the column 5 of Table 5, respectively. The temperature coeificients of permittivity are set forth in column 6 of Table 5. All the samples shown in the tables are desirable for use in a capacitor.

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. A sintered ceramic dielectric material consisting essentially of a perovskite-type compound of the chemical formula (Ba Na (Na ,,Nb )O wherein x ranges from 0.2 to 0.95.

2. A sintered ceramic dielectric material consisting essentially of a perovskite type compound of the chemical formula (Sr Li (Li Nb wherein x ranges from 0.2 to 0.95.

TABLE 1 First Final Power factor Temperature firing firing Permittivity at 20 C. coeflieient oi temperatemperaat 20 C. and 1 mHz. ermittivity Sample number Composition ture C.) ture C.) and 1 mHz. (X10- p.p.m./ C.)

71 (BamsNaom) (Nan.245Nbo 755)O 1, 100 1, 400 85 12 -50 79 (BannNaus)(NB-0.025Nbo.m)0a 1,000 1,200 400 35 +1,500

TABLE 2 First Final Power factor Tem erature firing firing Permittivity at 20 0. cos eient of temneratemperaat 20 C. and 1 mHz. ermittivity Sample number Composition ture C.) ture C.) and 1 mHz. (XIO- p.p.m./ C.)

81 (srossNamz) (N80.245Nb0.151)0s 1, 100 1, 4 0 75 12 ---60 39 MNaM)(N80.021Nb0.u1a)01 1,000 1,200 300 40 +1, 800

TABLE 3 First Final Power factor Temperature firing firing Permittivity at 20 C. eoeflicient oi temperatemperaat 20 C. and 1 mHz. ennlttivity Composition ture C.) ture C.) and 1 mHz. X p.p.m./ C.)

-- r0.1s i0.o2) o.245Nbo.1s5)0a 100 1, 400 50 14 -60 (Sr Lio.1)(Li0.02rNb ,w5)Oz 1,000 1,200 200 +600 TABLE 4 M 1 3. A sintered ceramic dielectric material consisting es- Inga; 3 oxide (Bao) o 6 sentially of a perovskite type compound of the chemical- Sodium oxide (Na o) 051-0375;; formula x L-x) 025x 1-025x) 3: wherein x ranges Niobium oxide (Nb O 0.5-0.125x from 0.2 to 0.95.

' TABLE 5 Col. 1 Col. 2 Col. 3 C01. 4 Col. 5 Col. 6

7 (BamsNams) (N 0.2375N 0.7t25)03 1,100 1,320 90 7 50 73 (BamNfion) (NflmzsN .7100: 1, 050 1,270 100 4 -50 ,050 1, 250 150 5 --40 1, 050 1, 250 200 6 20 1, 050 1, 250 250 7 1, 050 1, 240 350 8 +400 1 000 1, 220 400 10 +800 msN Ms) 0.2375N 0.7fl25)Ol 1,100 1, 350 so 8 0.1 0.1) (N o.22sNbo.71s 0: 1, 050 1,300 5 -60 (Sro.iNan.z) (NamNbmot 1, 050 1,270 130 5 -50 O.1Nau.a) 0.175N 0.825)0: 1,050 1,270 180 7 -40 (Sio.sN8o.5) (N a0.125Nbo,g 5)Oa 1, 050 1, 270 230 8 +60 (S MNaoJ) (N80.075Nb0,02s)0a 1, 000 1, 250 300 9 +500 rmNaM) (N80.05N 0.95)0z 1 000 1, 230 320 10 +1, 000

005 001) 0.2a11N o.1e21)0: 1, 1,320 60 10 -50 00 0.!) 0 .225Nb0 715)03 1,050 1,270 80 8 40 00 00) 0.zN 0.a)O3 1,050 1,250 5 40 oJ M) o.11sNbo.a2s)0a 1,050 1,250 4 20 (S M M) tJ.125N O.B75) 1, 050 1,250 200 3 +10 o.a o.7) iomNbmoor 1, 050 1, 240 280 5 +150 98 (Slo,2Llo,a) (Li0.05Nb0.0s)Oa 1,000 1, 220 300 8 +300 References Cited UNITED STATES PATENTS 2,452,532 10/ 1948 Wainer 10639 R 3,502,598 3/1970 Nitta et al. 252-62.9 2,864,713 12/1958 Lewis 1 39 R 3,231,799 1/ 1966 Prokopowicz et al. 10639 R OTHER REFERENCES Wemple, S. H. et a1.: Relationship Between Linear and Quadratic Electra-Optic Coefiicients in Ferroelectrics in Appl. Phys. Letters, March 1968, pp. 209- Evans: Introduction to Crystal Chemistry; Cambridge,

TOBIAS E. LEVOW, Primary Examiner W. R. SATTERFIELD, Assistant Examiner U.S. Cl. X.R. 

